Manufacture of cylindrical objects



y 1938. F. w. WHITEHEAD ET AL. 2,118,959

MANUFACTURE OF CYLINDRICAL OBJECTS Filed NOV. 22, 1937 Patented May 31, 1938 UNITED STATES MANUFACTURE OF CYLINDRICAL OBJECTS Frederick William Whitehead and William Thomas Goodby, Bristol, England, assignors to The Bristol Aeroplane Company Limited,

Gloucester, England, a British company Application November 22, 1937, Serial No. 175,962 In Great Britain February 26, 1936 2 Claims.

of five and a half inches diameter which has been subjected to a nitriding treatment of surface hardening may be found to have been deformed by as much as one hundredth of an inch.

According to the present invention, a method of restoring to circularity a sleeve or the like which has been deformed as above described consists in operating upon it in a centreless grinding machine of which the working wheel is a burnishing wheel and removing thereby an amount of material less than the amount, which would have to be removed to restore the sleeve to circularity by mere removal of material. This operation, herein termed straightening, has the effect of restoring the circularity of the sleeve despite the fact that very little material is removed from it. For example, to correct a deformation of one hundredth of .an inch, the straightening operation may remove as little as one quarter to one half of a thousandth of an inch. The straightening operation is preferably applied only to the outer surface but it is found that the circularity of the inner surface is restored also.

This phenomenon is believed to be due to the result of surface traction between the working wheel and the sleeve.

The operation is not an ordinary grinding operation. If the sleeve were ground, in the ordinary way, to such an extent as to remove the deformation, it would have to be ground both on the external and on the internal surfaces in order that the uniform thickness of wall should bemaintained, and such grinding would locally remove the very thin hardened nitrided layer.

With the present invention the nitrided layer is not penetrated to any serious extent.

The treatment according to the invention is distinguished from a rolling operation in that the burnishing wheel is rotated at a high speed and at a speed greater than the speed of rotation of the control wheel.

As shown in the accompanying drawing, the sleeve It! may be supported on the V-shaped block ll of an ordinary centreless grinder. A regulating or control wheel l2 bears against the sleeve and controls the speed of its rotation. Straightening is effected primarily by a burnishing wheel l3 of larger diameter (referred to above as the working wheel). Where the sleeve I0 is about five and a half inches in diameter, the control wheel I2 may be ten inches in diameter, and the burnishing wheel l3 twenty inches in diameter. The wheels and the sleeve rotate, in the ordinary way, as shown by the arrows. The wheel l2 may be driven at 40 R. P. M. and the burnishing wheel l3 at 950 to 1,000 R. P. M. When the wheels and the sleeve are rotating in this way, the sleeve rises by a few 'thousandths of an inch from the left-hand side of the V-shaped block, as shown greatly exaggerated in the drawing.

Both the wheels l2 and !3 may be composed of fine abrasive grains embodied in a moderately hard vitrified bond.

The invention may also be used for treating hollow cylindrical bodies, other than sleeves, such as the cylinder liners for internal-combustion engines.

We claim:

1. The herein-described method of restoring to circularity a hollow cylindrical object which has been deformed by a case-hardening treatment, which consists in operating upon it in a centreless grinding machine of which the working wheel is a burnishing wheel of very fine abrasive, grinding the external case of said object by said burnishing wheel to remove an amount of material from the object less than the thickness of the case whereby the grinding operation does not perforate the case and removing only such an amount of material from the external part of the case which is less than the amount which would have to be removed to restore the object to circularity by mere removal of material, and operating by pressure of said burnishing wheel through said case upon the body of metal in the object below the case for forcing such body and the case at points of protuberance back into a condition of circularity.

2. The herein-described method of restoring to circularity an internal combustion engine sleeve-valve, which has been deformed by being nitrided, which consists in operating upon its outer surface in a centreless grinding machine, removing from the outer surface of the case an amount of material less than the amount which would have to be removed therefrom to restore the sleeve to circularity by mere removal of material and less than the thickness of the case whereby the removing operation will not perforate the case, and simultaneously with the removing operation causing the material of the object beneath the case to flow until the outer surface of the object is truly circular, whereby the protuberances of the sleeve valve will be pressed partially back into a condition of near circularity made into complete circularity by the concomittant removing action from the case.

FREDERICK WILLIAM WHITEHEAD. WILLIAM THOMAS GOODBY. 

